1. Field of the Invention
The present invention relates to surface-modified fillers and a process for modifying the surfaces of fillers using a water-based organosiloxane-containing composition; wherein the organosiloxanes are soluble in water and contain OH groups and at least one amino-functional group and, optionally, at least one functional group from the series consisting of alkyl, haloalkyl, alkenyl, glycidyl ether alkyl, acryloxyalkyl and methacryloxyalkyl, wherein one of tide functional groups is bonded to each silicon atom of the organosiloxane. The present invention also relates to the use of the surface-modified fillers and to compounds containing the surface-modified fillers and an ethylenevinyl acetate copolymer.
2. Discussion of the Background
In general, fillers are used as additives, inter alia for adhesives, sealants, polymer compositions and paints. These fillers are normally inorganic materials, it being possible to choose between inactive and active products, Fillers can be used to modify specific mechanical and/or physical properties of a polymer matrix: the so called "reinforcing fillers". Since the reinforcing function can vary, a definition is only possible in conjunction with the polymer used in each case. In the case of rubber and synthetic elastomers, it is possible, for example, to vary the properties of hardness, strength, elasticity and elongation.
Reinforcing fillers, apart trom pyrogenic silica and carbon black, have hitherto played a relatively unimportant role, however, and, until recently, fillers have been used mainly as extenders in order to prepare products at lower cost. The increase in price of base polymers, however, has led to a reconsideration of the role of fillers, Nowadays, the aim is rather to maintain the balance between cost and performance through the targeted replacement of the base polymers with specially coated fillers.
Although pretreated fillers are more expensive than the conventional types, their prices are not drastically increased as a result of coating since great effects and improvements can be achieved using small amounts of coating material.
Using the preparation of alumimnum hydroxide as an example, the above situation may be briefly illustrated. Aluminum hydroxide (ATH), in the form of ground or as finely divided crystals, is used as a filler and flame retardant wherever the processing temperatures are not significantly above 200.degree. C. ATH is halogen-free, noncorrosive, nontoxic, physiologically acceptable and highly efficient in reducing smoke density.
ATH is offered in a variety of qualities, matched to the particular properties of important plastics systems. ATH can be incorporated in high filling contents from 50 to 70%) in elastomers to be crosslinked, thermoplastics and thermoplastic elastomers, duromers, PVC, ethylene-vinyl acetate copolymers and dispersions.
Fillers are usually modified in an additional process step either after drying the mineral or after processing it by grinding (cf. FIG.1): Diagram 1: Diagram of the preparation of silanized aluminum hydroxide ##STR1##
Silanization is typically carried out either dry (spraying the alkoxysilane into special mixing units), wet/slurry (application of an aqueous or alcoholic silane/solvent mixture), direct (the addition of liquid silane during compounding) or by spraying a silane emulsion onto the heated filler.
For work-up, many mineral fillers, after their separation from gangue and impurities, are slurried with water, hydroclassified and dried.
Thus, the surface properties of fillers can be modified by treatment with organoalkoxysilanes, organoalkoxysilane mixtres or organoalkoxysilane polycondensates, which are optionally present in dissolved form in organic solvents (U.S. Pat. No. 5,571,851, EP 0 632 109 A1, EP 0 590 270 A2, EP 0 492 223 A2, WO 90/02779). In these cases, when water or hydroxyl groups are present, significant amounts of alcohol arm liberated by hydrolysis. Moreover, processes in which organic solvents are present can usually only be carried out with special, cost-intensive safety measures.
EP 0 716 128 A2, FP 0 716 127 A2, EP 0 675 128 A1 and the as yet unpublished German Patent Application No. 196 39 782.0 disclose stable compositions of water-soluble organosiloxanes which are used, inter alia, for the silanization of fillers. Such water-based systems, when diluted with water, do not liberate any alcohols by hydrolysis.
U.S. Pat. No. 5,543,173 discloses a method for reducing the tendency of inorganic powders, for example aluminum hydroxide, to agglomerate, which includes treating the powder with an optionally alcohol-containing solution including organosiloxanes that can be obtained by hydrolysis of an organotrialkoxysilane, for example a vinyltialkoxysilane, an alkyltrialkoxysilane, a haloalkyltrialkoxysilane or an epoxy-, methacryloxy- or an amino-functional trialkoxysilane, the degree of oligomerization being greater than 2 and below the gel point, and then subsequently drying the treated powder. According to U.S. Pat. No. 5,543,173, powders treated in this way can be used in polymer blends.